Some internal combustion engines utilize a compression device such as a turbocharger to increase engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to an exhaust manifold side of an engine and the compressor is coupled to an intake manifold side of the engine. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure (e.g. boost, or boost pressure) in the intake manifold and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, for example with a wastegate. An actuator may be operatively coupled via a linkage to a wastegate valve and driven to position the wastegate valve anywhere between a fully open position and a fully closed position (e.g., at a valve seat) to achieve the desired boost based on operating conditions. The actuator may be an electric actuator such as an electric motor, for example.
Electric wastegate actuators are designed to be able to place a wastegate valve at the fully closed position so that maximum boost may be delivered to an engine when desired. As exhaust pressure acts against the wastegate valve, continuous application of current to the wastegate actuator is required to provide an adequate force opposing the exhaust pressure and to maintain the wastegate valve at the fully closed position. The current required to maintain the wastegate valve at the fully closed position will vary throughout the course of operation as the exhaust pressure acting against the valve, and the pressure differential across the valve, varies as well.
In some approaches, a DC current is applied to the electric wastegate actuator to maintain the wastegate valve at the fully closed position when placement at the fully closed position is desired. The DC current is the current sufficient to maintain the wastegate valve at the fully closed position with the maximum potential exhaust pressure acting against the valve. In other words, the DC current is selected based on worst-case operating conditions. As such, the DC current often exceeds the current that is merely sufficient to maintain placement at the fully closed position, as the instant exhaust pressure acting against the valve is frequently less than the maximum potential exhaust pressure.
The inventors herein have recognized several issues with the approach identified above. Because the DC current frequently exceeds that which would be sufficient to maintain the wastegate valve fully closed, the wastegate actuator consumes an excessive amount of power. Further, the use of excessive current to hold the wastegate valve fully closed imposes excessive force on the wastegate valve and potentially other parts of the wastegate assembly (e.g., a linkage coupling an output end of the wastegate actuator to the valve), in turn imposing a high degree of mechanical stress thereon. Still further, excessive current consumption leads to increased heating of the wastegate actuator, causing the actuator to approach its maximum acceptable operating temperature sooner than would otherwise be the case.
One approach that at least partially addresses the above issues includes a method of operating a wastegate, comprising determining a holding current with which to hold a wastegate valve at a desired position, the holding current determined based on a pressure differential across the wastegate valve.
In a more specific example, the desired position is a fully closed position.
In another aspect of the example, the pressure differential is determined based on turbine inlet pressure and turbine outlet pressure.
In yet another aspect of the example, determining the holding current includes for a first range of engine speeds, weighting an average pressure differential across the wastegate valve greater than a peak pressure differential across the wastegate valve, and, for a second range of engine speeds, weighting the peak pressure differential greater than the average pressure differential, the first range of engine speeds being greater than the second range of engine speeds.
In still another aspect of the example, the holding current is adjusted based on one or both of engine speed and load.
In this way, excessive power consumption by a wastegate actuator, excessive heat generation in the actuator, and excessive mechanical stress imposed on a wastegate valve may be mitigated. Thus, the technical result is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.